Availability

mission capable rateavailablemission capablemission-capable rateAvailability (Reliability Engineering)Mission-Capableoperational availabilityoperational readinessPartially mission capablesystem readiness
In reliability theory and reliability engineering, the term availability has the following meanings:wikipedia
186 Related Articles

High availability

high-availabilityavailabilityfive nines
In high availability applications, a metric known as nines, corresponding to the number of nines following the decimal point, is used.
Availability refers to the ability of the user community to obtain a service or good, access the system, whether to submit new work, update or alter existing work, or collect the results of previous work.

Reliability engineering

reliabilityreliability theoryreliable
In reliability theory and reliability engineering, the term availability has the following meanings:
Reliability is closely related to availability, which is typically described as the ability of a component or system to function at a specified moment or interval of time.

Unavailability

The degree to which a system, subsystem or equipment is in a specified operable and committable state at the start of a mission, when the mission is called for at an unknown, i.e. a random, time. Simply put, availability is the proportion of time a system is in a functioning condition. This is often described as a mission capable rate. Mathematically, this is expressed as 100% minus unavailability.
It opposes availability.

Downtime

network outagescheduled downtimeoutage
Availability measures are classified by either the time interval of interest or the mechanisms for the system downtime.
Reliability, availability, recovery, and unavailability are related concepts.

Lockheed Martin F-22 Raptor

F-22 RaptorF-22F-22A Raptor
Lack of repair facilities and tools – also lack software development (e.g. software caused many delays in the DoD F22 Raptor program),
Effectively maintaining the stealth features can decrease the F-22's mission capable rate to 62–70%.

Mean time to repair

MTTR
Inherent availability is generally derived from analysis of an engineering design and is calculated as the mean time to failure (MTTF) divided by the mean time to failure plus the mean time to repair (MTTR).
MTTR is often part of a maintenance contract, where a system whose MTTR is 24 hours is generally more valuable than for one of 7 days if mean time between failures is equal, because its Operational Availability is higher.

List of system quality attributes

ilitiesquality attributesRAMS
List of system quality attributes
availability

Optimal maintenance

Availability is well established in the literature of stochastic modeling and optimal maintenance.
Cost functions depending on the reliability, availability and maintainability characteristics of the system of interest determine the parameters to minimize.

Spare part

sparepartsPart
Availability considered in maintenance modeling can be found in Barlow and Proschan [1975] for replacement models, Fawzi and Hawkes [1991] for an R-out-of-N system with spares and repairs, Fawzi and Hawkes [1990] for a series system with replacement and repair, Iyer [1992] for imperfect repair models, Murdock [1995] for age replacement preventive maintenance models, Nachlas [1998, 1989] for preventive maintenance models, and Wang and Pham [1996] for imperfect maintenance models.
As a result, operational availability is impaired.

Systems engineering

systems engineersystemssystem engineering
Refer to Systems engineering for more details
Reliability engineering is the discipline of ensuring a system meets customer expectations for reliability throughout its life; i.e., it does not fail more frequently than expected. Next to prediction of failure, it is just as much about prevention of failure. Reliability engineering applies to all aspects of the system. It is closely associated with maintainability, availability (dependability or RAMS preferred by some), and logistics engineering. Reliability engineering is always a critical component of safety engineering, as in failure modes and effects analysis (FMEA) and hazard fault tree analysis, and of security engineering.

RAMS

RAM
RAMS
RAMS is an acronym for Reliability, Availability, Maintainability, and Safety.

Generating Availability Data System

Generating Availability Data System (Electricity Industry)
For example, the North American Electric Reliability Corporation implemented the Generating Availability Data System in 1982.
*Availability

Decimal

base 10decimal fractiondecimal system
However, typical availability values are specified in decimal (such as 0.9998).

System

systemssubsystemsubsystems
The degree to which a system, subsystem or equipment is in a specified operable and committable state at the start of a mission, when the mission is called for at an unknown, i.e. a random, time. Simply put, availability is the proportion of time a system is in a functioning condition. This is often described as a mission capable rate. Mathematically, this is expressed as 100% minus unavailability.

Execution unit

functional unitexecution unitsEUs
The ratio of (a) the total time a functional unit is capable of being used during a given interval to (b) the length of the interval.

United States Department of Defense

Department of DefenseU.S. Department of DefenseDoD
Lack of repair facilities and tools – also lack software development (e.g. software caused many delays in the DoD F22 Raptor program),

Fault tree analysis

fault treeevent treesfault tree analysis (FTA)
Fault tree analysis and related software are developed to calculate (analytic or by simulation) availability of a system or a functional failure condition within a system including many factors like:

Mean time between failures

MTBFmean time to failuremean time between failure
Inherent availability is generally derived from analysis of an engineering design and is calculated as the mean time to failure (MTTF) divided by the mean time to failure plus the mean time to repair (MTTR).

Stochastic modelling (insurance)

stochastic modelingstochastic modelling
Availability is well established in the literature of stochastic modeling and optimal maintenance.

Power station

power plantpower plantspower stations
Availability is used extensively in power plant engineering.

North American Electric Reliability Corporation

NERCNorth American Electric Reliability Corporation (NERC)North American
For example, the North American Electric Reliability Corporation implemented the Generating Availability Data System in 1982.

Condition-based maintenance

maintenancecondition based maintenancecondition-based maintenance (CBM)
Condition-based maintenance